Shell and tube heat exchangers are widely used in industry for heating, cooling, condensing and evaporating fluids by flowing one fluid through the tubes (tube side) and a second fluid through the shell outside the tubes (shell side). The heat exchanger must be carefully engineered for the service intended to provide maximum efficiency in transfer of heat through the tube walls and between the shell side fluid and the tube side fluid. The present invention is concerned with mechanical support for the tubes in a manner to suppress destructive vibration thereof and with improved baffling of shell side for improved turbulence of that fluid to maximize heat transfer while reducing pressure drop across the shell to minimize pumping costs.
It is usual to provide baffles on the shell side. Conventionally, these are baffle plates extending from alternate sides of the shell interior across the tubes. Such baffles are provided with suitable openings for the tubes. Plate baffles support the tubes and partially determine the heat duty of the exchanger by the spacing between the baffles. To increase heat duty, the spacing between baffles must be reduced thereby increasing the number of passes across the tubes by the shell side fluid. Usually, a higher shell pressure drop tends to offset the so obtained gain in heat duty.
It will be apparent that, back of each plate baffle in the direction of shell side flow, there will exist an area of stagnation such that the total area of heat transfer wall of the tubes is reduced by the extent of such area in the "dead spaces" back of baffles.
In addition it is found that the flow of shell side fluid across the tubes tends to cause the same to vibrate. Each tube will have characteristic frequencies of vibration depending upon unsupported length and the like. Excitation of low frequency natural periods of vibration can cause excessive wear of tube walls at the points of passage through plate baffles. Premature failure of tubes from this cause has been frequently observed. See "Acoustic Vibrations in Tubular Exchangers", E. A. Barrington, Chem. Eng. Progr., Vol. 69, pages 62-68 (July, 1973).
An advance in tube support is described in U.S. Pat. No. 3,708,142, Small. The system set out in the Small patent is also discussed in "Tube Vibration In A Thermosiphon Reboiler", J. F. Eilers & W. M. Small, Chem. Eng. Progr., Vol. 69, pages 57-61, (July, 1973). The arrangement so described provides lengths of bar stock extending across the tube bundle in the spaces between columns of tubes and the spaces between rows of tubes. The rods are passed through every such space and welded at their ends to a metal strip about the bundle which assumes an elliptical form because the rods are spaced longitudinally of the tube bundle.